The effects of Hurricane Dean on seafloor pressure, atmospheric pressure and coastal water levels

On August 18, 2007 at approximately 1300 UTC, Dean, then a Category 4 hurricane moving west-northwest across the central Caribbean, passed approximately 15 nautical miles south of buoy 42407, a Deep-ocean Assessment and Reporting of Tsunamis (DART™) station. With an eyewall radius of 10 nautical miles, this is the first occurrence of a hurricane's maximum winds passing over an operational DART™ station. Designed to operate in conditions of up to a Beaufort 9 (41-47 knots), the DART™ station successfully transmitted its data, despite the pounding it received from Hurricane Dean.

DART™ systems consist of a seafloor Bottom Pressure Recorder (BPR) and a surface buoy. The BPR converts measured pressure and temperature to an estimated water level, using a factor of 670 mm/psia, and then transmits these estimates to the surface buoy via an underwater acoustic modem. The surface buoy then serves as a communications transceiver and forwards the water level estimates to NOAA's National Data Buoy Center (NDBC). The BPR at 42407 lies at a depth of 4528 meters.

At an NDBC weather buoy (42059) about 45 miles east of 42407, atmospheric pressure dropped to 972.9 hPa at 09:50 UTC, 3 hours before Hurricane Dean passed near the DART™ buoy. The inverse barometer effect (1 cm per hPa) would indicate a surge on the order of 30 cm. As the hurricane passed, the residual (observed minus predicted tide) water levels at the DART™ buoy showed only a 2-cm estimated surge following the pressure drop at 42059. Results of the preliminary analysis are provided.

The water level stations operated by NOAA's Center for Operational Oceanographic Products and Services (CO-OPS) in Puerto Rico and the U.S. Virgin Islands, about 200 nautical miles north of the DART™ buoy, recorded elevated water levels of about 0.18 m (0.59 ft) on average. The highest water levels of 0.25 m (0.83 ft) above predicted tide occurred at Magueyes Island, PR on August 18 at 20:30 UTC